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Old 08-19-2010, 11:01 AM   #1
buzzstpoint
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Default HP L1740 Monitor doesn't light up

So here's the deal.

The display will power up but you dont see anything on the screen.
But if you hold a flashlight to the screen you can see the image on the screen.

I've browsed through the forum and seen some posts about the Benq board. But it seems i don't have one of those boards. From the pics here it doesn't match what I have. The boards dont have any visual cracks or burn spots. on it.

Also the monitor had issue for awhile. The screen would be dark r if it was turned off. You would have to switch it on and off several times. You would see the screen then it would go dark. After a dozen on/off the screen would light up. Now it completely went out and not coming back.
Any help on what to test would be great.
Here's what I got.

HP L1740
Assy # 374166-201
Spares 396638-001
Rev ITYG001

Any ideas on what to test? I don't have testing equipment but digital and analog multimeters.

Last edited by buzzstpoint; 08-19-2010 at 11:07 AM..
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Old 08-19-2010, 11:16 AM   #2
retiredcaps
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Default Re: HP L1740 Monitor doesn't light up

Quote:
Originally Posted by buzzstpoint View Post
But if you hold a flashlight to the screen you can see the image on the screen.

But it seems i don't have one of those boards. From the pics here it doesn't match what I have.
Post a clear focused picture of your boards after reading this

http://www.badcaps.net/forum/showthread.php?t=1868

Post a top down view of both sides (all boards).

Quote:
Any ideas on what to test? I don't have testing equipment but digital and analog multimeters.
Yes, we have suggestions, but we need a picture to get a sense on where to begin.

Last edited by retiredcaps; 08-19-2010 at 11:21 AM..
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Old 08-19-2010, 11:49 AM   #3
buzzstpoint
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Default Re: HP L1740 Monitor doesn't light up

Roger that..

I'll get the image up tonight.
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Old 08-19-2010, 12:47 PM   #4
retiredcaps
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Default Re: HP L1740 Monitor doesn't light up

Quote:
Originally Posted by buzzstpoint View Post
I'll get the image up tonight.
I'll be out when the pics are probably posted, but from your description in post #1 "Now it completely went out and not coming back", I would check (power off, lcd unplugged)

1) fuse usually a picofuse. A good fuse should measure 0.3 ohms.

2) c5707 transistors. You can measure the resistance to see if it is shorted. pin 1-2, 1-3, and 2-3. Any reading below 100 ohms suggests it is shorted. To be 100% sure, you will have to remove the suspicious transistor and test it out of circuit.

3) fu9024 fets. Test the same way as transistors described above.
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Old 08-20-2010, 04:50 PM   #5
George Ortiz
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Default Re: HP L1740 Monitor doesn't light up

From what I've seen on this model of monitors. Depending on what time frame, there's at least three different type of power supplies. LG Phillips (that's the model I am having problems with (4) monitors), Benq, and another one (I own this one-problems with this one two) 715G1955-1.
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Old 08-23-2010, 09:31 AM   #6
buzzstpoint
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Default Re: HP L1740 Monitor doesn't light up

Sorry for the delay.. Family weekend.

Here's the pics of the board..




I've heard of the PICO fuse..

Where is that located?
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Old 08-23-2010, 09:46 AM   #7
retiredcaps
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Default Re: HP L1740 Monitor doesn't light up

Quote:
Originally Posted by buzzstpoint View Post
Sorry for the delay.. Family weekend.

I've heard of the PICO fuse..

Where is that located?
Well, you definitely have at least 2 bad caps. See pic where I marked it.

Your pics are a bit small (low resolution) so the other caps could be bad, but I can't tell due to flash and low resolution.

A picofuse is used on some boards (not all) and usually labeled with PF.

To get replacement caps, follow PlainBill's post at

http://www.badcaps.net/forum/showpos...33&postcount=2
Attached Images
File Type: jpg PICT1213-bloated.jpg (96.2 KB, 43 views)
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Old 08-23-2010, 09:56 AM   #8
buzzstpoint
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Default Re: HP L1740 Monitor doesn't light up

The other 3 tall caps don't look like those 2.
The 2 you circled are bumped up on top. The other three are flat.
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Old 08-23-2010, 10:04 AM   #9
retiredcaps
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Default Re: HP L1740 Monitor doesn't light up

Quote:
Originally Posted by buzzstpoint View Post
The other 3 tall caps don't look like those 2.
The 2 you circled are bumped up on top. The other three are flat.
You will learn that caps don't have to be bloated to be bad. They can have high ESR (ohms) or be out of tolerance.

For example, a 2200uF 35V cap may meausre 300uF.

Given how cheap caps are (less than 60 cents each), most here will recommend that you recap ALL caps. You don't have that many on your board so an extra $1.80 (3 * 60 cents) isn't going to break the bank.

edit: Don't forget the small one just north (above) the big blue cap. You can leave the big blue cap alone. It is rarely bad (but not never).
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Old 08-23-2010, 10:08 AM   #10
buzzstpoint
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Default Re: HP L1740 Monitor doesn't light up

Ok, I'm off the Digikey.
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Old 08-23-2010, 10:38 AM   #11
buzzstpoint
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Default Re: HP L1740 Monitor doesn't light up

Hit quote instead of Edit....


All caps have been ordered.. Let you know by the end of the week.. (if the caps come in)
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Old 08-24-2010, 02:09 PM   #12
tigertamer
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Default Re: HP L1740 Monitor doesn't light up

Digi-Key is faster than Santa Claus!

Tigertamer
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Old 08-26-2010, 06:50 AM   #13
buzzstpoint
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Default Re: HP L1740 Monitor doesn't light up

Yup, I already had an account there. I order parts for my hotel TV's.
Just got the caps in yesterday, but they shorted me one cap. Everything says 3 caps, but only 2 in the bag.
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Old 08-26-2010, 09:54 AM   #14
retiredcaps
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Default Re: HP L1740 Monitor doesn't light up

Quote:
Originally Posted by buzzstpoint View Post
Just got the caps in yesterday, but they shorted me one cap. Everything says 3 caps, but only 2 in the bag.
Since 2 are obviously bad, you can change out those 2 and retest while waiting for the 3rd.
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Old 08-26-2010, 07:28 PM   #15
buzzstpoint
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Default Re: HP L1740 Monitor doesn't light up

All fixed!!

I replaced all the caps I had. Plugged it in and it lit right up.
Looks good and working great!!

I suppose I could let Digikey know they shorted me a cap. but it would probably cost me more in shipping to get that one cap. I replaced the 2 that you said were bad and left the one by the other 2 large.

Thanks to you I just bought a monitor for less then 10 bucks!!

Thanks a bunch.. You guys work on Televisions as well?
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Old 08-26-2010, 08:29 PM   #16
retiredcaps
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Default Re: HP L1740 Monitor doesn't light up

Quote:
Originally Posted by buzzstpoint View Post
I suppose I could let Digikey know they shorted me a cap. but it would probably cost me more in shipping to get that one cap.

You guys work on Televisions as well?
Glad you got it working.

If Digikey screwed up, I don't see why THEY wouldn't send you the other cap for free. Just send them an email explaining the short cap. Please report back on their reply because we recommend Digikey a lot. If they don't fix it, we can recommend other vendors.

Some members here are CRT experts and some are LCD/plasma gurus.
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Old 08-26-2010, 09:07 PM   #17
buzzstpoint
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Default Re: HP L1740 Monitor doesn't light up

Ok,

I sent an email to the customer support about the missing cap. I'll let you all know how they respond.
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Old 08-27-2010, 05:29 PM   #18
buzzstpoint
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Default Re: HP L1740 Monitor doesn't light up

Wonderful Customer Support..

Quote:
Hi Joe,

I just wanted to let you know that I did receive your email regarding the 1 pc of P10301-ND that was shorted from your order. I went ahead and shipped the 1 pc out today at no charge via UPS 2nd day so you should receive it on Tuesday. Of course we picked up the shipping, and I do apologize for our error. If there is anything else I can do to help please let me know.

Thank You,
**** ******

**** ******
Digi-Key Corporation
Customer Service Representative
1-800-344-4539

No argument or questions asked.. Two thumbs up!
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Old 08-27-2010, 05:37 PM   #19
retiredcaps
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Default Re: HP L1740 Monitor doesn't light up

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Originally Posted by buzzstpoint View Post
Wonderful Customer Support..
Good to know and I'm sure members can confidently keeping recommending digikey.com.

Now if only their shipping costs to Canada wasn't $8USD ...
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Old 10-23-2010, 05:45 PM   #20
Mike Toole
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Default Re: HP L1740 Monitor doesn't light up

Hey guys! Bumping this thread because I have the same issue with the same model. I popped the back off of the monitor and here's a picture.



I'm an absolute beginner when it comes to this stuff. I know what capacitors are and I've used a soldering iron before, but that's about as far as I go. But I got this monitor and another one with the same issue for free, and if it's a matter of replacing $5.00 worth of caps, I want to make a go of it.

Anyone up for helping? Where should I start? Or should I just replace all caps? Is there a visual guide for soldering/replacing caps?

TIA, this place is awesome and I've been reading about this particular phenomenon (bad caps killing the power to monitor backlights, making them seem horribly broken) for an hour. I'm going to start asking around my office to see if anyone else is having this issue.
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